engleski

Mechanism of crystallization of zeolite A microcrystals from initially clear aluminosilicate solution: A population balance analysis

Heating of the clear aluminosilicate solution (33.33Na2O• Al2O3• 3.33SiO2• 400H2O) from the room temperature (23o C) to the reaction one (40, 50 and 60oC) causes a spontaneous precipitation of an amorphous aluminosilicate (gel) and simultaneous formation of zeolite nuclei in the gel matrix. The amorphous aluminosilicate tends to dissolve immediately after the formation, which causes the releasing of nuclei from the gel matrix ant their growth. Growth of the nuclei (crystals) takes place by the reaction of monomeric and/or low-molecular aluminate and silicate species from the liquid phase on the surfaces of the growing zeolite crystals. However, the growth process, and thus the crystallization of zeolite A start at a time tc = tc(0) > 0. An analysis of the influence of the heating of the reaction mixture from the room temperature (23o C) to the reaction one (40, 50 and 60oC) have shown that this factor has a negligible influence on the "delaying" of the crystal growth and crystallization, respectively. Hence, it was concluded that the "delaying" of crystal growth and crystallization, respectively, was determined by the time needed for the formation of amorphous aluminosilicate (gel), formation of nuclei in the gel matrix and releasing of the nuclei during the gel matrix. The proposed mechanism of crystallization of zeolite A from clear aluminosilicate solution was confirmed by population balance analysis of the crystallization process at 40 and 60 degrees C.

Zeolite A ; crystallization ; clear solution ; mechanism ; population balance

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